Sound not coming from computer monitor?

So basically, I just got a used Dell u2415 computer monitor, and it has an hdmi input. I plugged in my snes mini, and video comes out. I know the monitor doesn't have built in speakers, so I got an external monitor speaker and plugged it in. It isn't making any noise. I don't know if since its used... show more So basically, I just got a used Dell u2415 computer monitor, and it has an hdmi input. I plugged in my snes mini, and video comes out. I know the monitor doesn't have built in speakers, so I got an external monitor speaker and plugged it in. It isn't making any noise. I don't know if since its used it's just not working, or there's something I don't know. Help!
Update: Edit: So I need to clarify that I'm NOT using this for a computer. I'm using this for gaming consoles, also, the computer has a 3.5 mm output jack, and the speakers are plugged into both to the monitor and an electrical source.
Update 2: Edit 2: I have googled the answer many times and gotten no answer. Also the speakers volume is at the max volume.
4 answers 4